Preheat your oven to 350℉. Coat the bottom and sides of an 8x8-inch square baking pan with cooking spray and line with parchment paper so that you have overhang on two sides, about 8 by 14 inches.

Melt the butter and 8 ounces of white chocolate in the microwave or using a heatproof bowl set over a pot of simmering water. Once melted, take the bowl away from the heat (if you used the stovetop method) and stir in the sugar and salt.

Whisk in the eggs one at a time followed by the vanilla extract and paste. Gently fold in the flour and when you have just a little bit left of the flour still unincorporated, add the remaining 2 ounces white chocolate. Transfer the batter into the prepared pan.

Distribute the lemon curd in about 5 or 6 equal portions with a spoon over the batter and swirl using a fork to partially incorporate into the batter. Bake for 25-28 minutes or until a toothpick inserted into the center comes out clean. Set the baking pan on a cooling rack and let the cake cool completely then lift the entire block out using the parchment paper and divide into small squares.

This cake is better the next day. If you have time, refrigerate the cake overnight and serve it at room temperature the next day.